1. Field of the Invention
The present invention relates to a package for an optical module for coupling a light emitting element, for example, a laser or the like with an optical fiber.
2. Description of the Related Art
A conventional package of this type, having a construction as shown in FIG. 2, is well known. FIG. 2 is a view showing a sectional structure of the conventional package for an optical module.
Referring to FIG. 2, reference numeral 1 is a package frame, 2 a bottom plate, and 3 a pipe fixedly attached to the package frame 1 passing through a predetermined region thereof A plate about 1 mm in thickness is normally used for the bottom plate 2 of the conventional package for the optical module. For the package frame 1, a frame in a square cylinder-like form about 1 mm in wall thickness on four sides is used.
In manufacturing the optical module by use of the package described above, a light emitting element 4 and a lens 5 for condensing light rays are mounted on a substrate 7 inside the package, and a single mode optical fiber 6 is fixedly attached to the extremity of the pipe 3.
In the optical module shown in FIG. 2, rays of light emitted from the light emitting element 4 are condensed by the lens 5, and coupled with the single mode optical fiber 6. Coupling of outgoing rays of light from the light emitting element 4 with the single mode optical fiber 6 is highly sensitive such that deviation of the single mode optical fiber 6 by mere several .mu.m causes deterioration in the coupling of the rays of light to a great extent. Deviation of the light emitting element 4 by about several .mu.m instead of the single mode optical fiber 6 also causes extreme deterioration in the coupling of the rays of light.
The package for the optical module shown in FIG. 2 has a drawback that it is vulnerable to a stress, and susceptible to various types of warps because it is provided with the package frame 1 in the order of several .mu.m in thickness, and only the lower edge of the package frame is securely attached to the bottom plate 2 having even thickness. As a result, the conventional package for the optical module has structural problems as described hereafter.
Firstly, the pipe 3 is fixedly attached to the package frame 1, and the single mode optical fiber 6 is fixedly attached to the pipe 3. As a result, warping of the package frame 1 causes the pipe 3 to be tilted, which in turn displaces the single mode optical fiber 6 from its optimum position, creating a cause for misalignment of the optical axis.
In particular, when fixedly attaching the single mode optical fiber 1 to the pipe 3, a large stress acts on the pipe 3 to hold it in place. The stress causes the package frame 1 to be warped. In such a case, the single mode fiber 6 securely fixed to the package frame 1 in a state as warped is consequently, displaced from the optimum position by the agency of reaction force to cause the package frame 1 to restore its original position. This is another cause for misalignment of the optical axis.
Furthermore, for securely mounting the package for the optical module on the surface of a fixture mount, flanges of the bottom plate 2 are fixedly attached thereto by screws. Accordingly, any warp of the surface of the fixture mount causes the bottom plate 2 to be warped, resulting in displacement of the light emitting element 4 (one of optical components). This is yet another cause for misalignment of the optical axis. In addition, warping of the bottom plate 2 causes also the package frame 1 to be warped.
As described in the foregoing, in the case of the conventional package for the optical module, intrinsic structural problems, that is, displacement of the optical components due to warping of the bottom plate and displacement of the pipe due to warping of the package frame create a direct cause for misalignment of the optical axis. In view of misalignment of the optical axis occurring due to warping of the package for the optical module as described above, it is necessary to reinforce the package for the optical module to prevent warping from occurring thereto even when a stress acts thereon.